Project Summary Severe injury and illness may lead to Acute Respiratory Distress Syndrome (ARDS), a high mortality acute respiratory failure that has an incidence of up to 80 cases per 100,000 person/years and a mortality rate of approximately 40%. The syndrome is associated with surfactant dysfunction and airspace edema that lead to alveolar collapse (derecruitment). Because of the degeneration of lung structure and function, mechanical ventilation is required to manage ARDS and maintain adequate gas exchange. However, mechanical ventilation induces ventilator-induced lung injury (VILI) which exacerbates the effects of ARDS through tissue overdistension and the cyclic collapse and reopening of alveoli and distal airways. Great strides have been made in understanding the basic mechanisms of VILI so that ventilation may be prescribed to reduce VILI while maintaining gas exchange. However, these two demands are frequently in conflict and identifying optimal mechanical ventilation parameters remains a challenging task for even the most skilled clinician. Determining the mechanisms of injury, and thus protective ventilation patterns, is complicated by the spatiotemporal heterogeneity of ARDS and VILI. It is thought that this heterogeneity may contribute to the progression of these diseases through the physical interconnectivity of the delicate alveoli. In this scenario, reduced distensibility of a flooded or collapsed alveoli will increase the strain in adjacent patent regions. This proposal will therefore test the overall hypothesis that edema and cellular injury will start in high stress locations; these initially injured areas will create stress foci, which make the proximal areas highly susceptible to further injury. To test this hypothesis, we will use a combination of experimental and computational techniques to illustrate the existence of injury heterogeneity and its progression, quantify the influence of injured regions on new damage, and predict the mechanisms that cause injury to spread. Novel image analysis techniques and custom-built computer software will quantify the micro- and macro- scale distribution of cellular injury in mouse VILI. These measurements will, for the first time, quantify the spatial distribution of cellular-scale injury. To interpret these data, we will implement a new type of statistical model to determine the range and strength of interdependence between existing and new cellular injury. These simulations will allow interpretation of my experimental measurements and, in future studies, facilitate the identification of ventilation regimes that prevent the spread of injury to reduce ARDS mortality. Finally, novel formulations of a finite element alveolar network will be used to determine if the clustering of cell injury may be attributed increased mechanical strain caused by the physical interconnectivity of the alveoli. In addition to these scientific goals, this proposal will support the development of a promising young pulmonary researcher through didactic and mentored training in laboratory techniques, mathematics, and professional skills.